When image forming apparatuses such as copying machines and multifunction printers scan documents by, for example, an ADF (Auto Document Feeder) so as to carry out copying, scan to e-mail, or filing, a plurality of documents to be scanned may include both a one-sided document and a two-sided document. In such a case, the following operations are required: first, the one-sided document and the two-sided document are separated; then, respective documents are scanned; and subsequently the documents scanned are reordered in an original order.
When the one-sided document and the two-sided document that are not separated are scanned and printed, an unwanted blank sheet may be outputted. Further, when a blank color sheet is mixed in, color toner (or ink) may be wasted. In cases where documents are filed, a memory such as a hard disk may be unnecessarily used if a blank sheet is mixed in. In order to solve these problems, for example, a method disclosed in Patent Literature 1 is proposed. According to the method of Patent Literature 1, a user can select a blank-document-page skip mode and a blank-document-page insert mode. When the blank-document-page skip mode is selected, image data of a blank document is detected in image data by comparing the image data with blank reference data and image formation of the detected image data is skipped by discarding the detected image data. In cases where the blank-document-page insert mode is selected, blank page data is inserted when image formation is carried out.